High powered lasers are presently in an extremely active stage of development and it has already been proposed to use such lasers in various earth working applications. Examples may be found in the following two U.S. patents:
Snedden, U.S. Pat. No. 3,544,165, 1970; PA0 Gladstone, U.S. Pat. No. 3,539,221, 1970.
The problem in attempting to apply the teaching of such patents to drilling, for example a hole 30cm in diameter and 5km deep is that even by using the most advanced form of lasers known today too much energy would probably be required to vaporize a cylinder of that size from the earth's crust. Some other approach therefore, seems necessary in order to reduce the total amount of energy input required and hence the cost for boring a hole this size.